Carbon nanotubes (CNTs) are a novel and interesting
graphitic carbon material which, since its discovery (1, 2),
has attracted considerable attention due to its unique
structuralandphysicochemical properties.CNTsare basically
carbon macromolecules in the shape of a hollow cylinder,
usually capped at least at one end, and characterized by a
length-to-diameter ratio e106 (Figure 1); the diameter of a
nanotube ranges from a few to tens of nanometers, while its
length can reach up to several millimeters. According to their
structure, CNTs are categorized as single-walled (SW) or
multiwalled (MW), see Figure 1a and c, respectively. Each
wall consists of a flat molecular network of C atoms known
as graphene (graphite is the material composed of overlaying
graphene sheets), while CNT end caps include pentagonal
rings to fit the geodesic curvature. The interwall distance in
MWNTs is on the order of a few angstroms.